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        <h1 id="动机"><a href="#动机" class="headerlink" title="动机"></a>动机</h1><p>1.在软件构建过程中，如果某一特定领域的问题比较复杂，类似的结构不断重复出现，如果使用普通的编程方式来实现将面临非常频繁的变化。<br>2.在这种情况下，将特定领域的问题表达为某种语法规则下的句子，然后构建一个解释器来解释这样的句子，从而达到解决问题的目的。</p>
<a id="more"></a>
<hr>
<h1 id="模式定义"><a href="#模式定义" class="headerlink" title="模式定义"></a>模式定义</h1><p>给定一个语言，定义它的文法的一种表示，并定义一种解释器，这个解释器使用该表示来解释语言中的句子。</p>
<hr>
<h1 id="结构"><a href="#结构" class="headerlink" title="结构"></a>结构</h1><p><img src="/2019/06/26/designpatterninterpreter/interpreter.png" alt="解析器"></p>
<hr>
<h1 id="代码示例"><a href="#代码示例" class="headerlink" title="代码示例"></a>代码示例</h1><figure class="highlight c++"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br><span class="line">79</span><br><span class="line">80</span><br><span class="line">81</span><br><span class="line">82</span><br><span class="line">83</span><br><span class="line">84</span><br><span class="line">85</span><br><span class="line">86</span><br><span class="line">87</span><br><span class="line">88</span><br><span class="line">89</span><br><span class="line">90</span><br><span class="line">91</span><br><span class="line">92</span><br><span class="line">93</span><br><span class="line">94</span><br><span class="line">95</span><br><span class="line">96</span><br><span class="line">97</span><br><span class="line">98</span><br><span class="line">99</span><br><span class="line">100</span><br><span class="line">101</span><br><span class="line">102</span><br><span class="line">103</span><br><span class="line">104</span><br><span class="line">105</span><br><span class="line">106</span><br><span class="line">107</span><br><span class="line">108</span><br><span class="line">109</span><br><span class="line">110</span><br><span class="line">111</span><br><span class="line">112</span><br><span class="line">113</span><br><span class="line">114</span><br><span class="line">115</span><br><span class="line">116</span><br><span class="line">117</span><br><span class="line">118</span><br><span class="line">119</span><br><span class="line">120</span><br><span class="line">121</span><br><span class="line">122</span><br><span class="line">123</span><br><span class="line">124</span><br><span class="line">125</span><br><span class="line">126</span><br><span class="line">127</span><br><span class="line">128</span><br><span class="line">129</span><br><span class="line">130</span><br><span class="line">131</span><br><span class="line">132</span><br><span class="line">133</span><br><span class="line">134</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">&lt;iostream&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">&lt;map&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">&lt;stack&gt;</span></span></span><br><span class="line"></span><br><span class="line"><span class="keyword">using</span> <span class="keyword">namespace</span> <span class="built_in">std</span>;</span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Expression</span></span></span><br><span class="line"><span class="class">&#123;</span></span><br><span class="line"><span class="keyword">public</span>:</span><br><span class="line">    <span class="function"><span class="keyword">virtual</span> <span class="keyword">int</span> <span class="title">interpreter</span><span class="params">(<span class="built_in">map</span>&lt;<span class="keyword">char</span>, <span class="keyword">int</span>&gt; var)</span> </span>= <span class="number">0</span>;</span><br><span class="line">    <span class="keyword">virtual</span> ~Expression() &#123;&#125;</span><br><span class="line">&#125;;</span><br><span class="line"></span><br><span class="line"><span class="comment">//变量表达式</span></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">VarExpression</span> :</span> <span class="keyword">public</span> Expression</span><br><span class="line">&#123;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">char</span> key;</span><br><span class="line"></span><br><span class="line"><span class="keyword">public</span>:</span><br><span class="line">    VarExpression(<span class="keyword">const</span> <span class="keyword">char</span> &amp;key)</span><br><span class="line">    &#123;</span><br><span class="line">        <span class="keyword">this</span>-&gt;key = key;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">int</span> <span class="title">interpreter</span><span class="params">(<span class="built_in">map</span>&lt;<span class="keyword">char</span>, <span class="keyword">int</span>&gt; var)</span> override</span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line">        <span class="keyword">return</span> var[key];</span><br><span class="line">    &#125;</span><br><span class="line">&#125;;</span><br><span class="line"></span><br><span class="line"><span class="comment">//符号表达式</span></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">SymbolExpression</span> :</span> <span class="keyword">public</span> Expression</span><br><span class="line">&#123;</span><br><span class="line"></span><br><span class="line">    <span class="comment">// 运算符左右两个参数</span></span><br><span class="line"><span class="keyword">protected</span>:</span><br><span class="line">    Expression *left;</span><br><span class="line">    Expression *right;</span><br><span class="line"></span><br><span class="line"><span class="keyword">public</span>:</span><br><span class="line">    SymbolExpression(Expression *left, Expression *right) : left(left), right(right)</span><br><span class="line">    &#123;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;;</span><br><span class="line"></span><br><span class="line"><span class="comment">//加法运算</span></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">AddExpression</span> :</span> <span class="keyword">public</span> SymbolExpression</span><br><span class="line">&#123;</span><br><span class="line"></span><br><span class="line"><span class="keyword">public</span>:</span><br><span class="line">    AddExpression(Expression *left, Expression *right) : SymbolExpression(left, right)</span><br><span class="line">    &#123;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">int</span> <span class="title">interpreter</span><span class="params">(<span class="built_in">map</span>&lt;<span class="keyword">char</span>, <span class="keyword">int</span>&gt; var)</span> override</span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line">        <span class="keyword">return</span> left-&gt;interpreter(var) + right-&gt;interpreter(var);</span><br><span class="line">    &#125;</span><br><span class="line">&#125;;</span><br><span class="line"></span><br><span class="line"><span class="comment">//减法运算</span></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">SubExpression</span> :</span> <span class="keyword">public</span> SymbolExpression</span><br><span class="line">&#123;</span><br><span class="line"></span><br><span class="line"><span class="keyword">public</span>:</span><br><span class="line">    SubExpression(Expression *left, Expression *right) : SymbolExpression(left, right)</span><br><span class="line">    &#123;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">int</span> <span class="title">interpreter</span><span class="params">(<span class="built_in">map</span>&lt;<span class="keyword">char</span>, <span class="keyword">int</span>&gt; var)</span> override</span></span><br><span class="line"><span class="function">    </span>&#123;</span><br><span class="line">        <span class="keyword">return</span> left-&gt;interpreter(var) - right-&gt;interpreter(var);</span><br><span class="line">    &#125;</span><br><span class="line">&#125;;</span><br><span class="line"></span><br><span class="line"><span class="function">Expression *<span class="title">analyse</span><span class="params">(<span class="built_in">string</span> expStr)</span></span></span><br><span class="line"><span class="function"></span>&#123;</span><br><span class="line"></span><br><span class="line">    <span class="built_in">stack</span>&lt;Expression *&gt; expStack;</span><br><span class="line">    Expression *left = <span class="literal">nullptr</span>;</span><br><span class="line">    Expression *right = <span class="literal">nullptr</span>;</span><br><span class="line">    <span class="keyword">for</span> (<span class="keyword">int</span> i = <span class="number">0</span>; i &lt; expStr.size(); i++)</span><br><span class="line">    &#123;</span><br><span class="line">        <span class="keyword">switch</span> (expStr[i])</span><br><span class="line">        &#123;</span><br><span class="line">        <span class="keyword">case</span> <span class="string">'+'</span>:</span><br><span class="line">            <span class="comment">// 加法运算</span></span><br><span class="line">            left = expStack.top();</span><br><span class="line">            right = <span class="keyword">new</span> VarExpression(expStr[++i]);</span><br><span class="line">            expStack.push(<span class="keyword">new</span> AddExpression(left, right));</span><br><span class="line">            <span class="keyword">break</span>;</span><br><span class="line">        <span class="keyword">case</span> <span class="string">'-'</span>:</span><br><span class="line">            <span class="comment">// 减法运算</span></span><br><span class="line">            left = expStack.top();</span><br><span class="line">            right = <span class="keyword">new</span> VarExpression(expStr[++i]);</span><br><span class="line">            expStack.push(<span class="keyword">new</span> SubExpression(left, right));</span><br><span class="line">            <span class="keyword">break</span>;</span><br><span class="line">        <span class="keyword">default</span>:</span><br><span class="line">            <span class="comment">// 变量表达式</span></span><br><span class="line">            expStack.push(<span class="keyword">new</span> VarExpression(expStr[i]));</span><br><span class="line">        &#125;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    Expression *expression = expStack.top();</span><br><span class="line"></span><br><span class="line">    <span class="keyword">return</span> expression;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">void</span> <span class="title">release</span><span class="params">(Expression *expression)</span></span></span><br><span class="line"><span class="function"></span>&#123;</span><br><span class="line"></span><br><span class="line">    <span class="comment">//释放表达式树的节点内存...</span></span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">main</span><span class="params">(<span class="keyword">int</span> argc, <span class="keyword">const</span> <span class="keyword">char</span> *argv[])</span></span></span><br><span class="line"><span class="function"></span>&#123;</span><br><span class="line"></span><br><span class="line">    <span class="built_in">string</span> expStr = <span class="string">"a+b-c+d-e"</span>;</span><br><span class="line">    <span class="built_in">map</span>&lt;<span class="keyword">char</span>, <span class="keyword">int</span>&gt; var;</span><br><span class="line">    var.insert(make_pair(<span class="string">'a'</span>, <span class="number">5</span>));</span><br><span class="line">    var.insert(make_pair(<span class="string">'b'</span>, <span class="number">2</span>));</span><br><span class="line">    var.insert(make_pair(<span class="string">'c'</span>, <span class="number">1</span>));</span><br><span class="line">    var.insert(make_pair(<span class="string">'d'</span>, <span class="number">6</span>));</span><br><span class="line">    var.insert(make_pair(<span class="string">'e'</span>, <span class="number">10</span>));</span><br><span class="line"></span><br><span class="line">    Expression *expression = analyse(expStr);</span><br><span class="line"></span><br><span class="line">    <span class="keyword">int</span> result = expression-&gt;interpreter(var);</span><br><span class="line"></span><br><span class="line">    <span class="built_in">cout</span> &lt;&lt; result &lt;&lt; <span class="built_in">endl</span>;</span><br><span class="line"></span><br><span class="line">    release(expression);</span><br><span class="line"></span><br><span class="line">    <span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<hr>
<h1 id="总结"><a href="#总结" class="headerlink" title="总结"></a>总结</h1><p>1.Interpreter模式的应用场合是Interpreter模式应用中的难点，只有满足“业务规则频繁变化，且类似的结构不断重复出现，并且容易抽象为语法规则的问题”才适合使用Interpreter模式。</p>
<p>2.使用Interpreter模式来表示文法规则，从而可以使用面向对象技巧来方便地“扩展”文法。</p>
<p>3.Interpreter模式比较适合简单的文法表示，对复杂的文法表示，Interpreter模式会产生比较大的类层次结构，需要求助于语法分析生成器这样的标准工具。</p>

      
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              <div class="post-toc-content"><ol class="nav"><li class="nav-item nav-level-1"><a class="nav-link" href="#动机"><span class="nav-number">1.</span> <span class="nav-text">动机</span></a></li><li class="nav-item nav-level-1"><a class="nav-link" href="#模式定义"><span class="nav-number">2.</span> <span class="nav-text">模式定义</span></a></li><li class="nav-item nav-level-1"><a class="nav-link" href="#结构"><span class="nav-number">3.</span> <span class="nav-text">结构</span></a></li><li class="nav-item nav-level-1"><a class="nav-link" href="#代码示例"><span class="nav-number">4.</span> <span class="nav-text">代码示例</span></a></li><li class="nav-item nav-level-1"><a class="nav-link" href="#总结"><span class="nav-number">5.</span> <span class="nav-text">总结</span></a></li></ol></div>
            

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